Modern electronic apparatus require power supply regulation in small form factor, having high efficiency and including adaptability to various qualities of input power. One approach to providing efficient power supply regulation involves "switched capacitors" configured to provide a step-up (higher output voltage than input voltage) function in addition to regulating output voltage within predetermined limits. Another approach provides a step-down (lower output voltage than input voltage) function. These approaches typically do not allow power supplies to operate in both step-up and step-down modes. In one example, battery-powered equipment includes a switching power supply to allow tighter voltage regulation over the life of a battery charge by providing a step-down function. Battery discharge and equipment operation thus cease when the battery voltage falls to or below the target voltage. This is disadvantageous because useful battery life is shortened and because some types of batteries require deep cycling (total or nearly total discharge prior to recharge) for optimal operation and useful life.
A second disadvantage of many such supplies is that the input-output voltage ratio must be one of a set of discrete values generally related to the number of capacitors being switched (i.e., the discrete values are restricted to integers). In many applications, finer resolution (tighter regulation to a target parameter, e.g., output voltage) than this provides is desirable or necessary.
Thus, what is needed is a practical, economical apparatus and an accompanying method for providing both step-up and step-down power supply regulation and particularly allowing arbitrary choice of input-output voltage ratio together with small form factor and high conversion efficiency.